Asparagus-Cheese Tartines

thin asparagus spears

extra-virgin olive oil

large shallots, thinly sliced

Salt and freshly ground pepper

large plum tomatoes, sliced lengthwise 1/4 inch thick

3/4-inch-thick slices of peasant or Pullman sandwich bread

tapenade

1/8-inch-thick slices each of Italian fontina, fresh mozzarella and Gruyère cheese

very thin slices of prosciutto

Aged balsamic vinegar, for drizzling